Data Sufficiency: Average Sufficiency

Concept Explanation

Average DS questions hinge on whether statements provide enough data for sum ÷ count or weighted totals.

Standard Answer Choices

• A — Statement I alone is sufficient; Statement II alone is not.
• B — Statement II alone is sufficient; Statement I alone is not.
• C — Both together are sufficient, neither alone.
• D — Either statement alone is sufficient.
• E — Neither alone nor together is sufficient.

Average DS Focus

Use Average = Total ÷ Count. Weighted average needs each group’s size and average.

DS Decision Flow

1. State exactly what must be determined (number, ratio, yes/no, or comparison).
2. Test Statement I alone—sufficient or insufficient?
3. Test Statement II alone—sufficient or insufficient?
4. If neither alone works, combine both statements.
5. Choose A–E based on sufficiency; never pick a value when data do not fix it uniquely.

Common Traps in Average Problems

• Averaging averages without weights.
• Forgetting to update count when a value is added.
• Confusing median with arithmetic mean.